When someone tells you “I’m depressed” or “I had a depression and now it’s gone” be supportive and kind.
You won’t understand it. Don’t look for its reasons. Don’t analyse it. Don’t try to explain how to avoid depression or find a reason why it happened. It’s impossible to prevent it. We will never know why depression happens. Like extremely bad weather, it just comes and goes. Force of nature, we can’t control it.
Sad doesn’t mean bad. Don’t judge it. We getting ill sometimes and there’s nothing wrong in illness itself, it happens and it’s part of life. Depressed person are not to blame.
You can save a life. It won’t hurt to ask, “did you had suicidal thoughts?”. Offer your time and support, refer your friend to suicide prevention service like The American Foundation for Suicide Prevention or UK National Suicide prevention Alliance. Don’t let them go and disappear.